1. Field of the Invention
The present invention pertains to the art of electrometallurgy and more particularly to methods for electroslag remelting of metals. The invention may be employed in installations for producing ingots by electroslag remelting either of one consumable electrode, or of a plurality of groups of such electrodes.
It is common knowledge that the consumable electrode melting-down rate, and consequently the ingot build-up rate, is dependent upon the energy released in the slag bath: the higher the current and the voltage, the greater the ingot build-up rate. This means that increasing the ingot build-up rate entails a rise in the electric power consumption.
2. Description of the Prior Art
Various methods have been proposed to reduce the electric power consumption at a predetermined ingot build-up rate in the course of electroslag remelting. One of these involves an action upon the slag bath and metal pool with the use of an electromagnetic means, with the result that, at the same electric power consumption, the consumable electrode melting-down rate is accelerated as against that without such action. Employed as the electromagnetic means in this method are inductance coils installed outside the mould, as disclosed in British Pat. No. 1,335,383.
In other prior art electroslag remelting methods, accelerating the consumable electrode melting-down rate without increasing the electric power consumption is attained by imparting to the electrode, apart from its lowering as it melts down, an additional motion in the slag, which additional motion may be a rotary motion around the electrode axis, a vertical (U.S. Pat. No. 3,565,994) or a horizontal (British Pat. No. 1,202,192) oscillatory motion, or a motion along a closed path in a horizontal or a vertical plane. Another prior art method employs for the same purpose power modulation by varying the voltage and the current at definite time intervals, as disclosed in British Pat. No. 1,188,028.
The use of the methods referred to above calls for relatively complicated apparatus and hence entails a higher cost of the equipment and of the process of electroslag remelting of consumable electrodes as a whole.
U.S. Pat. No. 3,776,294 discloses a method for electroslag remelting of metals, consisting in that a gas or a gas mixture is blown into the slag bath in the course of melting of an electrode or electrodes. According to the method, a gas or a gas mixture is blown into the liquid slag in such a manner that the gas bubbles upwards through the liquid slag, thereby upgrading the metal refining quality. Alternatively, the gas may be blown in a jet directed with respect to the mould wall at an angle other than a right angle causing the slag to rotate around the electrode or electrodes and thereby improving the slag-metal interaction.
The velocity of such a slag motion in the zone adjacent the electrode or electrodes, however, is comparable with that of the convective motion and thus fails to appreciably affect the electrode melting-down rate and to markedly reduce the electric power consumption at the predetermined ingot build-up rate.
In the electroslag remelting by the prior art methods of a plurality of consumable electrodes differing in cross-section, the melting-down rates of the electrodes greatly differ from one another, which is particularly pronounced when such electrodes are connected to opposite poles of a current source. This impairs the metal refining quality. Resorting to various electrical-engineering means, such as an equalizing wire connecting the bottom plate to the centre point of the transformer secondary winding, has shown these to be inadequate for equalizing the melting-down rates of electrodes differing in cross-section.